Method of drying synthetic rubber material

ABSTRACT

A method of drying synthetic rubber materials, which comprises contacting a moisture-containing synthetic rubber material with superheated steam at a temperature which is higher than the condensing temperature of steam, such condensing temperature being higher than 100*C., and up to 500*C.

United States Patent Takase et a1.

METHOD OF DRYING SYNTHETIC RUBBER MATERIAL Inventors: Katsuyasu Takase, Yuzo Nakane, Masamichi Yomura, all of Tokyo, Japan Assignee: The Japanese Geon 1 Co., Ltd.

and The Futaba Netsukagaku Kenkyujo Ltdgbo thof Tokyoflfapan Filed: March 12, 1971 Appl. No.: 123,719

US. Cl ..34/36 Int. Cl ..F26b 3/00 Field of Search ..34/l4, 17, 36, 37, 70, 15

Primary ExaminerCarro11 B. Dority, Jr. Attorney-Sherman and Shalloway [57] ABSTRACT A method of drying synthetic rubber materials, which comprises contacting a moisture-containing synthetic rubber material with superheated steam at a temperature which is higher than the condensing temperature of steam, such condensing temperature being higher than 100C., and up to 500C.

4 Claims, 1 Drawing Figure METHOD OF DRYING SYNTHETIC RUBBER MATERIAL This invention relate to a method of drying a moisture-containing synthetic rubber material within short periods of time.

Drying of synthetic rubbers has been previously preformed by a batch or continuous through circulation drying apparatus, a screw extrusion (rotary) drying apparatus, an expansion drying apparatus, a drum drying apparatus, a vacuum drying apparatus or combinations of these.

The continuous through circulation drying apparatus is adapted to dry a moisture-containing rubber material by passing heated air through the bed of moistened materials. Generally, the moistened materials are loaded in a thickness of 30 to 150 mm on a single endless horizontal conveyor consisting of wire-mesh screen or perforated apron and heated air is forcedly passed through the material bed from above or below. The drying time of about 40 to 120 minutes is required. For a large throughput of material, two or more high conveyors may be employed.

The flash (pneumatic conveyor) drying apparatus brings a turbulent current of drying air into direct contact with wet materials to evaporate the moisture. In this apparatus, air acts as a heat source, and serves to carry away the evaporated moisture and to transport the materials while performing the evaporation and drying. In this flash drying, the residence time of the materials in the apparatus, i.e. drying time, is as short as l to seconds.

According to the expansion drying apparatus, rubber materials having a water content of about 50 percent are squeezed to a water content of about 5 to percent by a screw-type extrusion squeezer. The rubber materials are then put into an expansion treating machine (expander), and usually heated to 110 to 230C. at a pressure of 30 to 100 kg/cm By a sudden release of the pressure, the materials are extruded through a narrow nozzle (the so-called expansion treatment). When the pressure is reduced, a greater part of the water contained in rubber is explosively evaporated, and the rubber materials become small spongy pieces having porous cells, which are then cooled to about 100C. or below by the evaporated water. Rubber particles released from the nozzle are put into a hot box (i.e., a chamber disposed at the rear of the nozzle plate and above the vibratory conveyor and maintained at a temperature above the condensing temperature by introduction of heated air), and then drop on the conveyor. The moisture remaining in the rubber particles is substantially completely evaporated while they are carried away on the conveyor and another conveyor connected to it. By this procedure, the rubber materials are dried to a water content of less than 0.5 percent which is a standard for ordinary synthetic rubbers.

In the conventional methods based on the utilization of the drying apparatus described above, rubber frequently sticks to the surface of the conveyor or the wall surfaces of the drying machine and sets to a solid mass of deposit within a short period of time. Since it must be removed frequently by hand, it becomes extremely difficult to operate the apparatus continuously.

The ease with which the rubber material sticks to the surface of the conveyor or the wall surfaces of the drying machine differs according to the inherent properties, shape, temperature and drying time of the rubber materials. However, the contamination of the inside of the drying apparatus, when it processes the same materials, is due most frequently to the fact that rubber which has been in long contact with the drying surface or wall surfaces deteriorates and becomes sticky. It is therefore desired to realize the drying of rubber materials within a short period of time, and to prevent the contamination of the inside of the drying apparatus by avoiding the deterioration of the rubber materials which are in contact with the drying surfaces and wall surfaces of the dryer.

A primary object of the present invention is to provide a method of drying synthetic rubber materials which effects the drying of rubber materials to low water contents within a very short period of time, and enhances the economy of the equipment.

A second object of the invention is to provide a method of drying synthetic rubber materials in which the drying apparatus is rendered operable in a continuous manner by preventing the deterioration of the deposit on the inner wall surfaces of the dryer and also the increase of the deposit.

It has been found that these objects of the invention can be achieved by a method comprising contacting a moisture-containing synthetic rubber material with superheated steam at a temperature which is higher than the condensing temperature of steam, such condensing temperature being higher than 100C. and up to 500C. preferably up to 200C. The method of the invention can be applied to the conventional drying apparatus such as the through circulation drying apparatus, expansion drying apparatus, or flash drying apparatus in which heated air is used as a heat transfer medium.

The accompanying drawing is a schematic illustrating the application of the drying method of the invention to an expansion drying apparatus.

Referring to the drawing, a moisture-containing synthetic rubber material to be dried is charged into an expander 1, and heated at a prescribed temperature and at a prescribed pressure. When the pressure is abruptly released, the rubber material is explosively discharged from the expander l, and is accumulated on a wire-mesh screen 3 within a chamber 2 as finely cut small particles 5. The particles 5 are dried by superheated steam introduced from an inlet 4. A part of the moisture in the synthetic rubber material is evaporated at the time of the explosive discharge.

In the conventional hot air drying of synthetic rubber materials, it is customary to employ a drying temperature in the vicinity of C. At higher temperatures, for example C., considerably longer periods of time are needed to dry the material to 0.5 percent or less for instance, and especially when the drying temperature is raised to C., it is impossible to dry the material to a water content of less then 0.5 percent. However, when the moisture-containing synthetic rubber material is contacted with superheated steam at a temperature higher than the condensing temperature of steam such condensing temperature being high than 100C. in accordance with the method of the present invention, the material can be dried to a water content of 0.5 percent or less even at a temperature as high as 130C. within a very short time. The time required is shorter than the conventional hot air drying method operated at about 80C., which has conventionally been regarded as opreduced. The temperature range specified in the present invention is not employed in the conventional method of removing the moisture of synthetic rubbers by heated air.

Drying time (minutes):

timum. 5 According to the invention, drying can be performed This fact is demonstrated by the experimental results within a short period of time by using superheated in the examples given later on, but is a new finding steam at elevated temperatures, and the continuous which cannot be expected from general common operation of the method has been made possible by knowledge that rubber materials tend to deteriorate in preventing the deposition of rubber. Since the method air at high temperatures. As will be clear from the comdoes not utilize hot air, the deterioration of the rubber parison of the results in Experiments 2 and 3 given i material can be prevented, and it is possible to avoid Table l, rubber materials containing large quantities of da g rs su h as m usti n. Th meth d is v ry us ful moisture can be dried in accordance with the method commerciallyof the present invention within a time about one-sixth The method of the lll'eseht invention enables a or less of the drying time that is required of the conven- Synthetic rubber material 10 be dried to a low water ti l d i h d d optinum conditions content at elevated temperatures within short periods Furthermore, it will be seen from the results of Experiof time, and therefore, is Particularly suitable for the ment 7 given in Table 2 that by the conventional heated y g of rubber which has a character of deteriorating air drying, it is impossible to dry a synthetic rubber y heat in and becoming y y- Examples of material to a water content of 0.5 percent or less at a the rubber materials that can be dried y the method of temperature of 130C. the invention include styrene-butadiene rubber, According to the invention, the rubber material is acrylonitrile-butadiene rubber, polybutadiene rubber, contacted with superheated steam at a temperature p lyi pr u r. y -p py rubber, higher than the condensing temperature of steam chloroprene rubber, and butyl rubber e The which is in excess of 100C., and up to 500C, vantages of the present invention show themselves repreferably up to 200C, to thereby dry the material to markably when drying polybutadiene rubber which has a water content of 0.5 percent or less within short a particularly large tendency to sticking, and periods of time. The contact time varies depending polyisoprene rubber which is particularly susceptible to upon such factors as the kind and bulk of rubber, or the 0 heat deterioration. The synthetic rubber materials to be temperature of superheated steam, but a time up to dried y be in Various forms Such as fine granules, minutes at the longest is sufficient for the purpose of Crumbs, P the present invention. If the inside of the drying ap- The following Examples will specifically illustrate the paratus is maintained at reduced pressure, it is not imn e possible to perform the drying of the material ata tem- EX M LE 1 perature lower than 100C. but higher than the dew A P point of steam. The employment of temperature higher About 2 g of each of the rubber specimens indicated than the condensing temperature of steam which is in in Table l were put into the expander 1 shown in the excess of 100C. is needed in order that the drying may 40 drawing, and heated at various temperatures and presbe carried out efficiently within short periods of time sures indicated in Table l. The pressure was abruptly while minimizing the deposition of rubber onto the released, and the specimen was explosively discharged inner wall surface of the dryer and preventing the into superheated steam (example of the present invendeterioration of the deposited rubber. The use of temtion) or heated air (control example) each maintained peratures in excess of 200C., especially in excess of at the temperatures indicated in Table l. The specimen 500C. or unnecessarily long contact with superheated was placed on wire-mesh screen 3 within chamber 2 as steam is not desirable since it may result in the fine particles 5, and dried by superheated steam or volatilization of an antioxidant contained in the rubber heated air introduced from an inlet 4 at the rate of 0.5. material and adversely affects the properties of the m/sec. The relation of the drying time to the water conrubber material. The economy of the method is also tent (heat loss) of the specimens is shown in Table 1.

TABLE 1 Present invention superheated steam Controls heated air Experiments numbers 1 2 3 Z 5 Rubber specimens 1 BR 1441 1 BR 1441 1 BR 1441 1 BR 1220 2 BR 1220 Water content of specimens (percent dry basis) 9. 2 9. 2 9. 2 14.5 10.0

Expander:

Tmnpcruture C.) 140 Pressure (kg/em!) 250 250 250 250 500 Drying temperature C.) 130 130 80 80 100 Water content (heat loss) percent 1 Nipol BR 1441 (aromatic oil-extended polybutadiene rubber, The Japanese Geon 00., Ltd.).

3 Trace.

The results shown in Table 1 demonstrate that the synthetic rubber was dried to a low content within a very short time of Experiments 1 and 2 (present invention) as compared with Experiment 3 (control example) in which severe expander conditions (higher temperature) and the drying temperature (80C.) which has conventionally been regarded as optimum were employed. Furthermore, when Experiment 5 is compared with Experiment 4, it will be seen that in the conventional methods, the drying was more difficult at a drying temperature of 100C. than at 80C.

EXAMPLE 2 Bulky crumb-like fragments of wet polyisoprene rubber having a moisture content of about 38 percent were charged into an extrusion drying provided with a 1.6 mm diameter die, and extruded while maintaining the temperature of the material at 130C. to form pellets of the rubber having a water content of 6.0 percent. The pellets were placed on wire-mesh screen 3 of the apparatus shown in the accompanying drawing, and dried by introducing superheated steam (example of the present invention) or heated air (control example) from inlet 4.

The relation among the drying temperature (the temperature inside the chamber 2 in the drawing), the drying time and the water content of the specimens is shown in Table 2.

It is seen from the results shown in Table 2 also that by the method of the present invention, the rubber is dried to a remarkably low water content with a short period of time, and that when heated air is used, it is,

impossible to dry the rubber at elevated temperatures.

TABLE 2 Present invention control 1. A method of drying synthetic rubber materials, which comprises contacting a moisture-containing synthetic rubber material with superheated steam at a temperature higher than the condensing temperature of said stream, said condensing temperature being higher than C., and up to 500C.

2. A method of drying synthetic rubber materials, which comprises contacting a moisture-containing synthetic rubber material with superheated steam at a temperature which is higher than the condensing temperature of said steam, said condensing temperature being higher than 100C., and up to 200C.

3. A method of claim 1, wherein said synthetic rubber material is polybutadiene.

4. A method of claim 1, wherein said synthetic rubber material is polyisoprene. 

1. A method of drying synthetic rubber materials, which comprises contacting a moisture-containing synthetic rubber material with superheated steam at a temperature higher than the condensing temperature of said stream, said condensing temperature being higher than 100*C., and up to 500*C.
 2. A method of drying synthetic rubber materials, which comprises contacting a moisture-containing synthetic rubber material with superheated steam at a temperature which is higher than the condensing temperature of said steam, said condensing temperature being higher than 100*C., and up to 200*C.
 3. A method of claim 1, wherein said synthetic rubber material is polybutadiene. 